J. E. GRAY. 561 



Class I. Antlio-Brachiophora= Cephalopoda, Cuv. 



Head very distinct, base with a cartilaginous ring ; eyes 

 2, lateral, very large ; arms 8, 10, round the mouth, armed 

 with suckers. (Antliae.) Branchia arborescent, 2-lobed, 

 close on each side, enclosed in the large sack-like mantle, 

 open above in front. Protectors, or shells, more or less 

 developed. 

 Order I. Anosteophora. Protectors 2; arms 8, equal; 



body finless. Gen. Octopoda. 

 Order II. Seplephora. Protectors horny or cretaceous ; 

 arms 10, 2 longer ; body 2-finnecl below. Gen. 

 Sepiola, Sepia. 

 Order III. Nautilophora. Protectors or shells many- 

 chambered, straight or discoidal ; arms 10, 2 

 longer ; body 2-finned below. Gen. Orthocera, 

 Spirula, Cristellaria, Spherula, Rotaclea, Nautilus, 

 Ammonita. 



Class II. GASTEROPODOPHORA=Gasteropoda, Cuv. 



Head distinct ; organs of vision 2, small ; foot flat, on the 

 ventral disk, formed for walking ; branchia more or less 

 developed ; mantle conical, sack-like ; protectors none, or 

 coriaceous, or shelly ; shell univalve, or many placed in a 

 series. 



Sub-class I. Pneumonobranchia. Branchia not de- 

 veloped ; breathing free air. 

 Order I. Adelopneumona. Branchia not developed ; pul- 

 monary vessels spread over the branchial cavity ; 

 branchial cavity closed by a valve : half hermaphro- 

 dite : operculum none : shell more or less developed, 

 not symmetrical, spiral ; aperture spread. Terres- 

 trial or aquatic, breathing free air. 

 (a.) Tentacula retractile, terrestrial. Gen. Limax or 

 Limacidea?, Onchidium, Plectophorus, Testacella, 

 Vitrina, Helix, Achatina, Clauselia. 

 (b.) Tentacula contractile, cylindrical ; amphibious. Auri- 

 cula, Carychium, Phytia. 

 (c.) Tentacula contractile, compressed ; aquatic. Lymnaea, 

 Planorbis, Ancyllus. 

 Order II. Phaneropneumana. Branchia not developed; 

 pulmonary vessels spread over the branchial cavity; 

 branchial cavity open : mantle free in front : uni- 

 sexual : operculum distinct : shell not symmetrical, 

 spiral ; aperture small. Terrestrial ; breathing free 

 air. Gen. Cyclostoma, Helicina. 



o o 



